KR20080061352A - Spark plug with welded sleeve on electrode - Google Patents

Abstract

A spark plug assembly (22) includes a center electrode (34) having a high performance metal sleeve (50) attached at its sparking end. The sleeve (50) is fitted to a tenon on the end of the center electrode (34) and fixed in place by a weld line (58) produced by laser beam pulses (56). The weld line (58) is applied by overlapping a plurality of spaced-apart beads in a single, continuous circumscribing line. The sleeve (50) is permitted to expand and contract under the influence of thermal cycling without constraint except for the fixation weld line (58). Therefore, the sleeve (50) does not experience stress build-ups resulting from differing rates of thermal expansion relative to the center electrode (34), which is preferably made from a nickel or other composition dissimilar to that of the high performance metal sleeve (50). Various ground electrode (30, 60) configurations are possible.

Description

SPARK PLUG WITH WELDED SLEEVE ON ELECTRODE}

This application claims the benefit of US Provisional Patent Application No. 60 / 721,821, filed September 29, 2005, entitled "LASER WELD OF AN IRIDIUM SLEEVE ONTO CENTER ELECTRODE."

The present invention relates to spark plugs for internal combustion engine engines, furnaces and the like, wherein the spark plug includes at least one electrode having a wear resistant sleeve welded thereto for enhanced durability and life.

In the field of spark plugs, there is a continuing need to improve the corrosion and corrosion resistance and to reduce the sparking voltage required to generate sparks in the gap between the center electrode and the ground electrode. Because of this, various designs have proposed using noble and / or precious metal ignition tips applied to standard metal electrodes. Typically, the ignition tip is pre-formed with a pad, rivet, or wire, which is then welded to the end of one or both of the center electrode, ground electrode.

Platinum and iridium alloys are the two precious metals commonly used for such ignition tips. Platinum-tungsten alloys have also been used with platinum-rhodium alloys and platinum-iridium-tungsten alloys. Other metals and / or alloys are also possible.

These precious metals and various other precious metal systems are typically present to provide acceptable spark plug performance, particularly regarding controlling spark performance and providing spark erosion and chemical corrosion protection, but current sparks using precious metal tips Plugs have a well-known performance limitation associated with relatively small spark surfaces, along with the methods used to attach precious metal components, including various types of welding. In particular, periodic thermal stress in an operating environment, such as due to mismatching of the coefficient of thermal expansion between base electrodes that is not similar to the electrode tip, can reduce service life. Typically, the electrode tip will be made of the precious metal and the precious metal alloy described above, and the base electrode will be made of nickel, nickel alloy, nickel plated copper, or other commonly used metal. The result of such mismatched temperature coefficients is a variety of other interaction phenomena that can cause cracks, thermal fatigue, and weld failure, and finally, failure of spark plugs.

This condition is particularly important in the field of industrial power generation, and the spark plug must be operated for an extended period of time in certain settings. In this type of application, mainly cited by way of example, it is desirable to tune the engine and its fuel supply with the ignition system very precisely in order to obtain the highest possible efficiency and fuel economy. Erosion and corrosion of the center and ground electrodes can affect the efficiency and performance characteristics of these engines. Therefore, there is a great need in the art to provide spark plugs with improved corrosion and corrosion resistance of sparking surfaces and related components.

The prior art has long considered this situation and has proposed a number of configurations employing precious metal components within the spark gap. For example, US Pat. No. 4,904,216 to Kagawa discloses a spark plug with a central electrode fitted with a tubular precious metal sleeve, attached by resistance welding, then pulled back and extruded into final form. . In another example, US Pat. No. 5,557,158 to Kanao discloses a spark plug comprising a center electrode fitted with a tubular precious metal sleeve. The sleeve is captured at the tenon end and then held in position through the cap. In another example, US Patent No. 6,064,114 to Knoll discloses a spark plug in which a tubular sleeve is fitted to a tenon on a central electrode and held in position by a compression cinch. This is followed by welding or soldering operations.

Therefore, it is highly desirable to develop a spark plug with a precious metal ignition tip in the form of a sleeve or other structure that is applied to the sparking end of the center electrode. However, prior art attempts have not considered the potential failure mechanisms associated with the attachment of dissimilar materials along the length, and the materials being exposed to intense thermal cycles. Thus, there is a need to develop a method of making a spark plug with an improved structure for improving spark plug performance and reliability while maintaining component integrity in extremely harmful operating environments.

The invention includes spark plug assemblies for spark ignition engines, furnaces and the like. The assembly includes a ground metal shell, including a ground electrode. The insulator body is at least partially disposed in this shell. The insulator body has an axial length and a central passage extending axially along the length. An electrically conductive center electrode is disposed in the central passage of the insulator body. The central electrode has an exposed length terminating at the distal tip. The center electrode is made of a first predetermined material composition. The sleeve is disposed around the exposed length of the center electrode and is made of a second material, which is not similar to the first material. The stationary welding line metallurgically joins the center electrode and the sleeve and is arranged in one transverse plane. When the center electrode and sleeve thermally expand and contract, they do not interfere with each other relative to each other along its entire interface length except in fixed welding. Therefore, the different ratio of thermal expansion between the center electrode and the sleeve will not limit the movement of the two components in the axis. According to the present invention, the tendency to proceed crack or thermal fatigue or other detrimental interaction phenomenon with respect to the center electrode will be much reduced.

The invention also includes methods of forming electrodes for spark plug assemblies as used in spark ignition engines, furnaces, and the like. The method includes providing a central electrode having an axial length terminating at the distal tip. The method also includes forming a tenon on the central electrode adjacent the distal tip, the tenon having an inset solder and an axially extending cheek. A sleeve having a base end and a free end is provided. The method includes sliding the sleeve onto the tenon, and contacting its base end with the shoulder of the tenon. A laser beam is provided. The method includes moving the laser beam in a relative path along the interface between the base end of the sleeve and the shoulder of the tenon to create a fixed welding line. The method serves only the stationary welding line to join the center electrode and sleeve so that the center electrode and the sleeve are free of thermal expansion and contraction relative to each other along their entire interface length except in the stationary welding line. That is, the method further includes installing in a spark ignition engine, a furnace, or the like.

Accordingly, the present invention defines a precious metal assembly and method that overcomes the disadvantages and drawbacks inherent in prior art designs. More specifically, the method allows the spark plug to operate for extended periods of time without catastrophic destruction by avoiding cracks, thermal fatigue, or other harmful interaction phenomena between the central electrode and its high performance sleeve component.

These and other features and advantages of the present invention will be more readily understood when considered in connection with the embodiments and the accompanying drawings.

1 is a cross-sectional view of a spark plug according to the present invention including one exemplary four-prong ground electrode as typically used in industrial engine applications,

2 is a side elevation view in a partial cross-sectional view of the central electrode assembly,

3 is a view of one end of a noble metal sleeve fixed to the distal end of the center electrode,

4 is a cross-sectional view generally taken along line 4-4 of FIG. 3,

5 is an enlarged view of the distal end portion of the central electrode, including the sleeve welded thereto;

FIG. 6 is a view of one end of the center electrode assembly as shown in FIG. 5,

7 is a cross-sectional view generally taken along line 7-7 of FIG. 6, illustrating weld zone penetration;

FIG. 8 is a partially cut cross-sectional view illustrating a weld formation in which continuous, overlapping and evenly spaced beads are located along a centerline where the bead may be set slightly below the sleeve / shoulder interface;

9 shows a laser welding setup for attaching a sleeve to the distal tip of a central electrode to achieve a desired welding formation,

10 is a cross sectional view of a second embodiment of the present invention in which an alternative annular ground electrode configuration is used in place of the four-prong type shown in FIG.

FIG. 11 is a cross sectional view of the lower end generally taken along line 11-11 of FIG. 10;

12 is an enlarged view of an alternative annular ground electrode, and

FIG. 13 is a side elevation view taken along line 13-13 of FIG. 12.

Referring to the drawings, like reference numerals refer to similar or corresponding parts throughout the several views, and a spark plug according to one exemplary embodiment of the present invention is generally shown in FIG. The spark plug 22 has a conductive metal shell 24 that is typically grounded when attached to an engine, furnace, or the like. The non-conductive insulator body 26 is disposed, at least in part, in the shell 24. The insulator body 26 has an axial length as formed by a central axis A extending longitudinally, which forms a vertical center line with respect to the spark plug assembly 22. The central passage 28 extends axially through the insulator body 26 and is located centrally along the central axis A. The electrically conductive ground electrode 30 is connected to the shell 24 and has a female or leg-shaped free end (or optionally ends) present in the spark gap. In the embodiment of Figure 1, the ground electrode 30 is shown in a so-called four-prong type, which is mainly used in industrial engine applications. As an alternative, the traditional single ground wire style can be used, as well as any other type of ground configuration. For example, FIGS. 10-13 illustrate alternative fully-ring type ground electrodes, as described in more detail below.

The spark plug 22 includes an upper terminal cap 32 fixed or held in the central passage 28 at the top end of the spark plug 22. The opposite lower end of the insulator body 26 is fitted to the central electrode assembly and is generally indicated by 34. Interconnecting the upper terminal cap 32 and the center electrode assembly 34 is a conductive spring connector 35. Of course, this is only one exemplary embodiment of a conductive electrical component included in insulator body 26. Those skilled in the art will know other arrangements and arrangements of components to achieve suitable high voltage conductive features included in insulator body 26. Returning to FIG. 1, in the embodiment as shown, a glass seal 36 is provided between the central electrode 34 and the insulator 26 to prevent leakage of combustion gases. Glass seal 36 may be modified to include an electrical noise suppression structure or other characteristics.

In FIG. 2, a central electrode assembly 34 having a body 38 that can be made of any material is shown in more detail, but a preferred embodiment consists of nickel or a nickel alloy. The central flange 40 forms an upper ledge 42 in which the upper pillar 44 of reduced diameter extends. In this embodiment, the upper pillar 44 penetrates the glass seal 36 and makes physical and electrical contact with the spring 35. The lower distal end of the body 38 is machined or formed into a round tenon shape with a shoulder 46 and a cheek 48. An optional undercut can be seen in the intersection of the shoulder 46 and the cheek 48. In an alternative configuration (not shown), the upper pillar 44 is omitted and the glass seal 36 is replaced with a fired-in suppressor seal (FIS). An alternative FISS design provides RFI suppression and forms a conductive path between the spring 35 and the center electrode assembly 34.

A tubular, cylindrical precious metal sleeve 50 is shown in FIGS. 3 and 4. Sleeve 50 may be made of an iridium alloy containing pure iridium, rhodium and tungsten, or other alloying elements. Alternatively, the sleeve 50 may be made of precious metals or alloys thereof to provide high performance, high erosion resistance and corrosion resistance over an extended service life. The inner diameter of the sleeve 50 is a loose fit to the tenant cheek 48 when the inner diameter of the sleeve 50 is at the minimum of its dimensional tolerance and the diameter of the tenon is at the maximum of its dimensional tolerance. fit or a slight interference fit.

Referring again to FIGS. 2 and 3, the sleeve 50 is shown to comprise a generally constant wall thickness extending between the base end 52 and the free end 54. The base end 52 abuts the shoulder 46 of Tenon when installed at the end of the central electrode assembly 34. If used, an undercut between the shoulder 46 and the cheek 48 will facilitate good and tight fitting of the base end 52 to the shoulder 46. The axial length of the sleeve 50 is generally the same as the axial length of the cheek 48 such that the free end 54 of the sleeve 50 is disposed in a common common transverse plane with the distal tip of the central electrode assembly 34. do. As best shown in FIG. 2, the body 38 of the central electrode assembly 34 has a major diameter that is generally the same as the major diameter of the sleeve 50. In practice, however, the wall thickness of the sleeve 50 may be slightly smaller than the radial width of the shoulder 46, so that even if there is some eccentricity in the sleeve 50 or the formed tenon, the center electrode 34 There may be a substantially continuous outer wall surface in the body 38. Thereby, a potential arrangement result is expected that the slightly reduced wall thickness in the sleeve 50 will never allow the insertion of the central electrode assembly 34 through the central passage 28 of the insulator body 26. In any case, the thickness of the sleeve 50 is of sufficient thickness to allow for the expected electrical corrosion over the lifetime of the spark plug 22, but is optimized to be thin enough to minimize internal stress and cost. Sleeve 50 may be manufactured by machining a sheet or rod, or by growing a carbon rod in an electroplating process, or by any other suitable technique.

Referring now to FIGS. 5-9, a method of attaching the sleeve 50 to the body 38 of the central electrode assembly 34 is shown. The sleeve 50 may be attached by any suitable welding operation after moving in contact with the shoulder 46 and positioned over the cheek 48 of tenon. Suitable welding techniques include, but are not limited to, laser welding, electron beam welding, and TIG welding, to name a few.

The following description represents one exemplary embodiment of the present invention. Most or all of this description depends on modifications, given changes in equipment, materials, choices, and other factors. In addition, these laser welding parameters have been optimized to increase weld transmission and strength and to reduce the splatter on the outside of the finished portion. The angle of incidence of the laser beam 56 is nominally perpendicular to the electrode surface, as shown in FIG. 9. The laser beam 56 is directed at 0.004 inches on the body 38 below the interface between the sleeve 50 and the shoulder 46. That is, while other arrangements may prove desirable in some situations, the centerline of the laser beam 56 is aimed at 0.004 inches below the shoulder 46. Satisfactory results were found using a laser welding process with the following parameters:

Welding energy: 1.6 Joules / pulse

As achieved, the directed beam 56 of the laser light source 56 causes an overlapping welding spot of a single bead targeted to fuse the sleeve 50 to the body 38, thereby fixing the welding line 58. ). In this configuration, a fixed welding line 58 can be achieved if the laser beam 56 is held stationary, and the electrode body 38 is maintained vertically in the collet and rotated for 1 to 4 turns. Of course, as an alternative, relative movement between the laser beam 56 and the electrode body 38 can be made by holding the electrode body 38 and moving the laser, or perhaps by moving both members at the same time. By following the above-described parameters, multiple overlapping laser welding of evenly spaced beads with weld bead diameters of approximately 0.02 inches, and spacings of approximately 0.008 inches or less can be achieved. This is shown in FIG.

Welded only at the bottom of the sleeve 50, ie at its base end 52. The free end 54 of the sleeve 50 is not welded or attached to the electrode assembly 34. This causes adjustment to the different thermal expansion rates between the body 38 and the sleeve 50. Therefore, the sleeve 50 is not limited in its axial direction unlike that by the fixed welding line 58. That is, welding only one end of the sleeve 50 means that its high performance composition thermally expands at a different rate than nickel or other dissimilar composition of the electrode assembly body 38 without creating stress in the sleeve 50. Let it contract The finished center electrode assembly 34 is then mainly from the edge of the center electrode, not from its tip, such as the four-prong structure shown in FIG. 1 and the annular structure shown in FIGS. 10-13. Used in one of various spark plug designs to propagate.

In the embodiment shown in FIGS. 10-13, the ground electrode, generally denoted by 60, is fixed to the lower end of the shell 24 by first resistance welding with a pocket formed at the bottom of the shell 24, and is inoperative. A turnover operation follows to mechanically lock the ground electrode 60 in position. The ground electrode 60 has a noble metal ring 62 surrounding the sleeve 50 on the central electrode 34 with a spark gap formed in the annular space therebetween. The ring 62 is held in a central position around the sleeve 50 in a hub like manner by a frame consisting of three spokes 64. Of course, more or less spokes 64 may be used, and in fact, it may be contemplated that in some applications, the frame may be a complete annulus without discernible gaps or spokes.

Various methods of forming the ground electrode 60 have been considered. In one embodiment, the spokes 64 are formed in separate operations, such as forging, machining, casting. Nickel would be a suitable material for making the spokes 64. In a similar manner, the noble metal ring 62, which is preferably iridium, can also be manufactured separately, and these two components are combined in subsequent operations, such as laser welding. However, other possible techniques for manufacturing ground electrode 60 are available. According to this alternative technique, a carbon rod (not shown) is placed in an electro-deposition tank containing an iridium rich (or other precious metal or alloy) bath or iridium anode. A suitable potential difference is formed between the carbon rod and the bath (or anode) such that elemental iridium (or other precious metal or alloy) is deposited and adhered to the outer periphery of the carbon rod to form an iridium shell. After the iridium shell achieves a sufficient thickness, the rod is removed from the bath and transferred to a new electro-deposition tank containing nickel rich bath or anode. Again, a potential is created between the rod and the bath (or anode), and nickel (or other selected metal) of the element deposits itself around the outside of the iridium shell and forms a nickel shell. After the nickel shell achieves a sufficient thickness, it is removed, cleaned and machined. The finishing operation includes forming a scallop along the length of the nickel shell. The slicing operation will then yield each wafer that will eventually be converted to ground electrode 60. At a suitable stage in accordance with the process, the carbon rod can be removed.

The purpose of using the sleeves 50 and 62 in the center and ground electrode assemblies 34 and 64 is to increase the life of these electrode assemblies and therefore to increase the overall life of the spark plug 22. The disclosed electrode design seeks to maximize the ground electrode surface area while maintaining good ventilation of the spark gap and to maintain a constant ground electrode gap with respect to the cylindrical surface of the central electrode 34. Therefore, if a continuous ring was not used for the ground electrode, the ground electrode could be formed to have an arcuate face and thereby maintain a constant gap over the entire spark gap.

The foregoing invention has been described in accordance with the relevant legal standards, and therefore, the description is intended to be illustrative rather than limiting in nature. It will be apparent to those skilled in the art that modifications and variations can be made in the disclosed embodiments, which are within the scope of the invention. Accordingly, the scope of legal protection of the invention can only be determined by the appended claims.

Claims (15)

Spark plug assembly for spark ignition engines, furnaces, etc., A ground metal shell comprising a ground electrode; An insulator at least partially disposed within the shell having an axial length and a central passage extending axially along the axial length; An electrically conductive central electrode having an exposed length terminating at the distal tip and having a first predetermined material composition disposed in the central passage of the insulator; A sleeve disposed about the exposed length of the center electrode, the sleeve being made of a second predetermined material that is not similar to the first predetermined material of the center electrode; And Metallurgically joining the sleeve and the center electrode and comprising a stationary welding line disposed in a single transverse plane, the center electrode and the sleeve being relatively unobstructed from each other along their interface length except in the stationary welding Spark plug assembly for spark ignition engines, furnaces, etc., characterized in that it is free of thermal expansion and contraction. 2. The spark plug assembly of claim 1 wherein the sleeve material is selected from the group consisting essentially of precious metals and alloys thereof. 2. The spark for an ignition engine, furnace or the like of claim 1, wherein said center electrode comprises tenon formed in said exposed length thereof, said tenon comprising a general transverse shoulder and a general axial cheek. Plug assembly. 4. The spark plug assembly for a spark ignition engine, furnace, or the like according to claim 3, wherein said cheek is of a general cylindrical shape and said shoulder is of a general annular shape. 5. The spark plug assembly of claim 4 comprising an undercut formation between the cheeks of the tenon and the shoulder of the tenon. 5. The spark plug of claim 4 wherein the sleeve has a general cylindrical configuration adapted to slide over the cheek of the tenon and with respect to the shoulder of the tenon. assembly. 7. The spark plug assembly of claim 6 wherein the stationary weld is disposed along an interface between the shoulder and the sleeve. 8. The spark ignition engine of claim 7, wherein the shoulder of the tannon includes a radial width and the fixed welding line radially penetrates the central electrode a distance longer than the radial width of the shoulder. Spark plug assemblies for furnaces and more. 8. The spark ignition engine of claim 7, wherein the exposed length of the center electrode has a major diameter and the sleeve has a major diameter generally equal to the major diameter of the exposed length of the center electrode. Spark plug assemblies for, or furnace etc. 8. The sleeve of claim 7, wherein the sleeve has a base end adjacent to the shoulder and a free end adjacent to the distal tip of the center electrode, wherein the sleeve has the free end of the sleeve generally with the distal tip of the center electrode. Spark plug assembly for a spark ignition engine, furnace, or the like, characterized in that it has an axis length generally equal to the axis length of the cheek to be disposed in a common transverse plane. A method of forming electrodes for a spark plug assembly for use in spark ignition engines, furnaces, and the like, Providing a central electrode having an axial length terminating at the distal tip; Forming a tenon on the center electrode adjacent the distal tip, the tenon having an inset shoulder and an axially extending cheek; Providing a sleeve having a base end and a free end; Sliding the sleeve over the tenon and contacting the base end of the sleeve and the shoulder of the tenon; Providing a laser beam; Moving the laser beam along an associated path along an interface between the base end of the sleeve and the shoulder of the tenon to create a fixed welding line; And Only the stationary welding line metallurgically couples the center electrode and uses the center electrode such that the center electrode and the sleeve are free of thermal expansion and contraction relative to each other along the entire interface length except at the stationary welding line. A method of forming an electrode for a spark plug assembly for use in a spark ignition engine, furnace, or the like, comprising the steps of: a. 12. The method of claim 11, wherein moving the laser beam comprises rotating the central electrode by at least 360 ° with respect to the beam. How to form. 12. The spark plug assembly of claim 11 wherein the step of providing the laser beam comprises directing the laser beam generally perpendicular to the axis of the central electrode. How to form an electrode for. 14. The spark plug of claim 13, wherein the step of providing the laser beam comprises directing the laser beam to the central electrode below the base end of the sleeve. A method of forming an electrode for an assembly. 12. The method of claim 11, wherein the stationary welding line radially penetrates the central electrode at a distance greater than the radial width of the sleeve. .

Images